The following is based on Korean Patent Application 99-18659 filed in the Republic of Korea on May 24, 1999, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a field emission array (FEA) using carbon nanotubes having characteristics of low work function, durability and thermal stability, and a method for fabricating the same.
2. Description of the Related Art
Carbon nanotubes, which were developed in 1991, are similar to fulleren (C6O). Since they have an excellent electron emission characteristic and chemical and mechanical durability, their physical properties and applications have steadily been studied.
A Spind""t-type field emission emitter, which is generally used for field emission displays, is composed of an emitter for emitting electrons and a gate for facilitating the emission of electrons. The emitter has a problem in that the life span of a tip is shortened due to atmosphere gases or a non-uniform electric field during operation. In addition, with such conventional metal emitter, a work function must be decreased to decrease the driving voltage, but there are limitations. To overcome this problem, fabrication of an electron emission source using carbon nanotubes which have a substantially high aspect ratio, an excellent durability due to their structure similar to that of C6O, and an excellent electron conductivity has been studied.
FIG. 1 is a schematic exploded perspective view of a field emission device using conventional carbon nanotubes which are disclosed in Appl. Phys. Lett., Vol. 72, No. 22, Jun. 1, 1998. As shown in FIG. 1, the field emission device using the conventional carbon nanotubes includes a front substrate 1 and a rear substrate 11 facing each other and anodes 2 and cathodes 12 which are formed on the front and rear substrates 1 and 11, respectively, in a striped pattern such that the anodes 2 cross the cathodes 12. The cathodes 12 are formed of carbon nanotubes in a structure in which grooves are formed on the rear substrate 11 in a striped pattern and the grooves are filled with a carbon nanotube-epoxy mixture. The anodes 2 are formed of an ITO film coated with phosphors.
FIG. 2A shows the steps of a method of fabricating the cathodes 12 on the rear substrate 11 of the field emission device of FIG. 1 using carbon nanotubes. FIG. 2B shows the steps of a method of fabricating the anodes 2 on the front substrate 1 of the field emission device of FIG. 1 using carbon nanotubes.
In fabricating the cathodes 12 using carbon nanotubes, grooves 12a, as shown in (b) of FIG. 2A, are formed in a striped pattern on a glass substrate 11xe2x80x2, as shown in (a) of FIG. 2A. Next, a carbon nanotube-epoxy mixture 12xe2x80x2 is deposited, as shown in (c) of FIG. 2A. Finally, the surface of the resulting structure is planarized to complete the cathodes 12, as shown in (d) of FIG. 2A.
In fabricating the anodes 2, an ITO film 2xe2x80x2 is deposited on the glass substrate 1, as shown in (a) of FIG. 2B. Next, as shown in (b) of FIG. 2B, the ITO film 2xe2x80x2 is etched in a striped pattern to form the anodes 2. As shown in (c) of FIG. 2B, the anodes 2 are coated with phosphors 3.
In fabricating cathodes using carbon nanotubes in such way, however, it is very difficult to align the carbon nanotubes in a single direction and to connect the carbon nanotubes to electrodes when manufacturing a device. Accordingly, this alignment problem must be overcome to substantially apply carbon nanotubes to a display device.
To solve the above problem, an object of the present invention is to provide a field emission array using carbon nanotubes, which can be easily aligned and closely contacts cathodes, and a method for fabricating the same.
To achieve the above object, the present invention provides a field emission array using carbon nanotubes. The field emission array includes front and rear substrates facing each other and separated by a predetermined distance; anodes and cathodes formed on the front and rear substrates facing each other, respectively, in a striped pattern, the anodes and the cathodes crossing each other; carbon nanotubes fixed on the cathodes corresponding to intersections between the cathodes and the anodes; and a metal fuser element for fixing the carbon nanotubes on the cathodes and conducting currents between the cathodes and the carbon nanotubes.
Preferably, the field emission array also includes an insulating layer deposited on the cathodes around the carbon nanotubes and the rear substrate, and gates formed on the insulating layer in a striped pattern to be parallel to the anodes. Each of the anodes is formed of an ITO film and coated with phosphor.
To achieve the above object, the present invention also provides a method of fabricating a field emission array using carbon nanotubes. The method includes the steps of: (a) forming cathodes on a rear substrate in a striped pattern; (b) printing a mixture of carbon nanotubes, metal powder and organic binder on predetermined areas of the cathodes; (c) vaporizing the organic binder by sintering the mixture and anchoring the carbon nanotubes on the cathodes by diffusing the metal powder; and (d) combining a front substrate, on which anodes are formed in a striped pattern, with the rear substrate having the cathodes on which the carbon nanotubes are anchored.
Preferably, the method also includes the steps of: forming an insulating layer on the tops of the cathodes other than portions to which the carbon nanotubes are to be adhered and on the top of the exposed rear substrate, before the step (b); and forming gates on the insulating layer after the step (c). At this time, the metal powder is composed of metal particles of a metal, selected from the group consisting of Ag, Al, Ni, Cu and Zn, having a diameter of 0.1-10 xcexcm and is diffused at a temperature of 250-500xc2x0 C.
Preferably, in the step (b), the metal powder is melted at a low temperature of 100-350xc2x0 C., and in the step (c), the mixture is sintered to evaporate the organic binder, and the low melting point metal powder is melted to anchor the carbon nanotubes on the cathodes. The metal powder is preferably composed of particles of a metal selected from the group consisting of Pb, In, InSn, PbSn, AuSn and a metal alloy thereof.
In the step (b), the organic binder is composed of at least one selected from the group consisting of xcex1-terpineol, ethyl cellulose and butyl carbitol acetate, and the printing is performed by an extrusion method using a filter for aligning the carbon nanotubes. Alternatively, in the step (b), the printing is performed by a screen printing method using a metal mesh screen which is patterned for aligning the carbon nanotubes. Preferably, in the step (c), the sintering is performed at a temperature of 200-500xc2x0 C.